The present invention generally relates to jitter compensation systems in rotary recording medium reproducing apparatuses, and more particularly to a jitter compensation system capable of performing jitter compensation by use of reference signals for tracking control which are reproduced from a rotary recording medium, in a rotary recording medium reproducing apparatus.
A new information signal recording and/or reproducing system has been proposed in U.S. Pat. No. 4,315,283 and No. 4,322,836, of which the assignee is the same as that of the present application. According to this proposed system, the recording system forms pits in accordance with an information signal being recorded along a spiral track on a flat rotary recording medium (hereinafter simply referred to as a disc), without forming a groove therein. In the reproducing system, a reproducing stylus traces over along this track to reproduce the recorded information signal in response to variations in electrostatic capacitance.
In the system, since no grooves for guiding the reproducing stylus are provided on the disc, it becomes necessary to record pilot or reference signals on or in the vicinity of a track of a program information signal, on the disc. Upon reproduction, the reference signals are reproduced together with the program information signal. Tracking control is carried out so that the reproducing stylus accurately traces along the track in response to the reproduced reference signals.
By use of this previously proposed system, there is no possibility whatsoever of the reproducing stylus or the disc being damaged since the recording track has no groove. The reproducing stylus can trace the same portion of the track repeatedly many times, whereby a special reproduction such as still, slow motion, or quick motion reproduction becomes possible in a case where the recorded information signal is a video signal. Moreover, operations such as a random access, highspeed search, and automatic cueing operation in which the reproducing stylus is shifted to a position of a desired recorded program where the reproduction is to be started, can be performed with ease.
However, in the reproducing apparatus, when irregularity (wow and flutter) exists in the rotation of the turntable which is placed with the disc to rotate the disc, eccentricity exists in the center hole of the disc, distortion is introduced in the disc upon molding of the disc, and the like, jitter (error in the time base) is introduced in the reproduced signal. The above jitter covers a frequency range from a relatively low frequency component corresponding to the rotational period of the disc due to such causes as the above irregular rotation and eccentric center hole, to as the above distortion in the disc, mainly, a few hundred Hz to 1.5 kHz.
In a case where the reproduced information signal is a color video signal, the above jitter gives rise to color shading, swinging of picture image in the reproduced picture of the receiver, and the quality of the reproduced picture greatly deteriorates.
There exists a conventional jitter compensation system in which the horizontal synchronizing signal is separated from a video signal reproduced from the disc by a reproducing transducer. In this system, the phase of the separated horizontal synchronizing signal is compared with that of a reference signal, and the jitter compensation is performed by displacing a reproducing element of the reproducing transducer along a relative scanning direction with respect to the disc in response to an output phase error signal obtained as a result of the phase comparison.
However, because the conventional jitter compensation system uses the horizontal synchronizing signal separated from the reproduced video signal, there is a disadvantage in that the system can only be applied to a reproducing apparatus for reproducing discs recorded with video signals.
On the other hand, in a case where the disc is recorded with a PMC audio signal as the information signal, the above conventional jitter compensation system cannot be employed because the horizontal synchronizing signal does not exist within the reproduced signal.
The PCM audio signal is normally recorded and reproduced by use of an interleaving system and a deinterleaving system. That is, in the recording system, an input analog signal is sampled for every appropriate time period in a sample-and-hold circuit, and the resulting sampled signal is converted into a modulated digital signal in an analog-to-digital (A/D) converter. This modulated digital signal is fed into a memory in which data write-in and read-out operations are controlled by a control pulse, and a series of word groups are arranged where the words obtained for every one sample of the digital signal respectively interleave with each other in a state separated from each other by a period of 10-odd H (H denotes one horizontal synchronizing period). Here, "one word" refers to the combination of bits obtained from one sample. The time period represented by 10-odd H, is determined in conformance with the format used.
A composite synchronizing signal is added to the signal thus obtained to produce a composite digital signal, which is then recorded on a magnetic tabe by a VTR. This rearrangement of the order of data is referred to as "interleaving". Since the interleaving of data results in the distribution of the signal information, even when the recorded or reproduced signal is deficient over one or more horizontal scanning (H) periods due to dropout, the associated signal present in the separate horizontal scanning period serves to reproduce the information.
A data part is extracted from the signal reproduced from the disc. This data part, which undergoes wave-shaping, is then converted into a binary coded digital signal, and thereafter supplied to a memory where the signal is written in and read out responsive to a control pulse and restored back into the original order. This restoring of the signal back into the original order, is called de-interleaving. The resulting signal is supplied to a digital-to-analog (D/A) converter where it is restored back into the original analog signal.
Conventionally, because the conventional jitter compensation system cannot be used for the above described reasons, when the above de-interleaving is performed in the reproducing system, the information signal which is reproduced in a state including the jitter component is written into a memory by de-interleaving with a constant clock signal. The information signal is read out from the above memory in the regular order by eliminating the jitter component. There fore, there was a disadvantage in that the memory needed a capacity obtained by adding the capacity for the jitter component to the capacity required to store the reproduced signal into the memory by de-interleaving.
Accordingly, a jitter compensation system was proposed in a United States Patent Application entitled "JITTER COMPENSATION SYSTEM IN A ROTARY RECORDING MEDIUM REPRODUCING APPARATUS" of which the assignee is the same as that of the present application. In this proposed system, reference signals recorded on the disc in a bursted manner with a predetermined period are reproduced, and a jitter compensation signal is obtained by comparing the phase of the reproduced reference signals and the phase of a standard signal having the same period as the above predetermined period, to perform jitter compensation by this jitter compensation signal. However, this system does not detect the period or frequency of the reference signals, but detects the period with which the reference signal is recorded in a bursted manner. Therefore, some problems are introduced in an attempt to obtain a jitter compensation signal having high signal-to-noise (S/N) ratio.